Conventional wind turbines generally include two or more turbine blades or vanes connected to a central hub. Each blade extends from the hub at a root of the blade and continues to a tip. A cross-section of the blade is defined as an airfoil. The shape of an airfoil may be defined in relationship to a chord line. The chord line is a measure or line connecting the leading edge of the airfoil with the trailing edge of the airfoil. The shape may be defined in the form of X and Y coordinates from the chord line. The X and Y coordinates generally are dimensionless. Likewise, the thickness of an airfoil refers to the distance between the upper surface and the lower surface of the airfoil and is expressed as a fraction of the chord length.
The inboard region, i.e., the area closest to the hub, generally requires the use of relatively thick foils (30%≦t/c≦40%). The aerodynamic performance of conventional airfoil designs, however, degrades rapidly for thicknesses greater than 30% of chord largely due to flow separation concerns. For thicknesses above 40% of chord, massive flow separation may be unavoidable such that the region of the blade may be aerodynamically compromised. It is noted that the turbine blade often has a circular cross-sectional shape along a connector portion of the turbine blade, which connects the inboard region of the turbine blade to the hub.
Thus, there is a need for an airfoil design that provides improved aerodynamic performance particularly with respect to the inboard region. Preferably, such a design would provide improved aerodynamic performance and efficiency while providing improved structural stiffness and integrity.